The present invention relates to radiation detectors. More specifically, but without limitation thereto, the present invention relates to a microminiature neutron detector for increasing the signal to noise ratio of ionization signals generated by incident radiation.
.sup.3 He neutron detector tubes are representative of the state of the art in detecting neutron radiation. The detection signals generated by such detectors may be calculated from the formula Vs=Qi/Ct, where Vs is the voltage signal generated by the detector, Qi is the charge induced by the incident neutron (typically about 20,000 electrons), and Ct is the capacitance of the detector. The capacitance of the detector has been a limiting factor in increasing the magnitude of Vs to a level above the noise from sources such as EMI, microphonics, thermal noise, and bias supply noise. A typical neutron detector tube rugged enough to withstand the high pressures required for neutron interaction (typically about 60 atm) and a volume large enough to provide counts significantly above the background level from neutron sources of interest is a concentric tubular capacitor about 18 inches in length. The capacitance of such a detector tube is about 20 Pf. The capacitance limits the typical voltage signal from such a detector tube to about 4 mV, which may be very difficult to distinguish from the noise background. A continuing need exists for a neutron detector having an output voltage signal level that may readily be distinguished from the noise background.